Alert archive / Missouri / Tornado Watches in 2011

Tornado Watch 420

June 2, 2011Calhoun County, Greene County, Jersey County, Illinois; 16 counties in Missouri

The Storm Prediction Center issued this tornado watch at Jun 2, 2011, 3:46 PM CDT for Calhoun County, Greene County, Jersey County, Illinois; 16 counties in Missouri. It was in force for 4 hr.

The area

The outline as issued.

The facts

Issued
Jun 2, 2011, 3:46 PM CDT (20:46 UTC)
Expired
Jun 2, 2011, 7:30 PM CDT
In force
4 hr
Issued by
the Storm Prediction Center
Largest hail expected
2 in
Strongest gust expected
60 kt

Counties Calhoun County, IL, Greene County, IL, Jersey County, IL, Audrain County, MO, Boone County, MO, Callaway County, MO, City of Saint Louis, MO, Franklin County, MO, Gasconade County, MO, Jefferson County, MO, Lincoln County, MO, Monroe County, MO, Montgomery County, MO, Osage County, MO, Pike County, MO, Ralls County, MO, Saint Charles County, MO, Saint Louis County, MO, Warren County, MO

The radar

The St Louis radar (KLSX), 79 km from the middle of the area, began a volume at 20:49 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

What SPC expected

The probabilities SPC published with the watch, for the watch area over its life.

Two or more tornadoes
40%
One or more EF2 to EF5 tornadoes
20%
Ten or more severe wind reports
30%
One or more gusts of 65 knots or more
30%
Ten or more severe hail reports
40%
One or more hailstones of 2 inches or more
30%
Six or more combined severe hail and wind reports
70%

Discussions around it

SPC mesoscale discussions over the same counties from four hours before the watch to its end.

The nearest sounding before it

Lincoln, IL (KILX), launched 12:00Z, 8.8 hours before the alert went out and 275 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-pSkew-T log-p diagram, Lincoln, IL at 12:00Z on 2011-06-02Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 0 joules per kilogram.LCL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Lincoln, IL at 12:00Z on 2011-06-02The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 65 square meters per square second.19395878Sfc1 km3 km6 km9 kmRMLM
The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.
Mixed-layer CAPE
0 J/kg
Mixed-layer CIN
No buoyant parcel
Mixed-layer LCL
0 m above ground
0-6 km bulk shear
26 kt
0-1 km storm-relative helicity
65 m²/s²
0-3 km storm-relative helicity
67 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

786 
WWUS20 KWNS 022039
SEL0
SPC WW 022039
ILZ000-MOZ000-030200-

URGENT - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 420
NWS STORM PREDICTION CENTER NORMAN OK
340 PM CDT THU JUN 2 2011

THE NWS STORM PREDICTION CENTER HAS ISSUED A
TORNADO WATCH FOR PORTIONS OF

       WEST CENTRAL ILLINOIS
       EAST CENTRAL MISSOURI

EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 340 PM UNTIL
900 PM CDT.

TORNADOES...HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND
GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE
AREAS.

THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 40 STATUTE
MILES NORTH AND SOUTH OF A LINE FROM 15 MILES NORTH NORTHWEST OF
COLUMBIA MISSOURI TO 10 MILES EAST NORTHEAST OF SAINT LOUIS
MISSOURI.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU0).

REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR
TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS.

OTHER WATCH INFORMATION...CONTINUE...WW 419...

DISCUSSION...A SMALL CLUSTER OF SEVERE/SUPERCELL THUNDERSTORMS HAVE
FORMED OVER CENTRAL MO...NEAR A REMNANT MCV.  THESE STORMS ARE
EXPECTED TO TRACK EASTWARD INTO THE WATCH AREA THIS
AFTERNOON...WHILE OTHER STORMS POTENTIALLY FORM ALONG OLD OUTFLOW
BOUNDARY EXTENDING FROM MCV TO SOUTH OF STL.  STRONG DEEP LAYER
EFFECTIVE SHEAR AND AMPLE CAPE WILL POSE A RISK OF SUPERCELLS
CAPABLE OF LARGE HAIL AND DAMAGING WINDS.  BACKED LOW LEVEL WINDS
NORTH OF THE OUTFLOW BOUNDARY COULD ALSO POSE A THREAT OF AN
ISOLATED TORNADO.

AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 2 INCHES. EXTREME TURBULENCE AND SURFACE
WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
500. MEAN STORM MOTION VECTOR 29025.


...HART

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Jun 2, 2:57 PM CDTMesoscale DiscussionSPCMonroe2 hr
Jun 2, 6:20 PM CDTMesoscale DiscussionSPCCalhoun, Jersey55 min

Nearby

Tornado Watches in Missouri, 2011Tornado Watches in Illinois, 2011Every tornado watch in 2011

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.